The purpose of this STTR is to produce a commercially available rapid-scan absorbance optical detection system for XLA/I analytical ultracentrifuges. The currently available absorbance optical system provided by the analytical ultracentrifuge manufacturer is not optimized for sedimentation velocity analysis, the most commonly used analytical ultracentrifugation (AUC) experimental method in biomedical research. AUC is becoming the method of choice for: 1) the analysis of interacting complex systems, 2) QA/QC of biopharmaceutical products, 3) the characterization of vaccines, 4) the characterization of particle size distributions of virus solutions, and 5) the development of drug formulations. The federal Food and Drug Administration increasingly recommends that protein biologics be characterized by sedimentation velocity. It is essential that the data acquisition and manipulation software be modernized to minimize the potential for serious errors in the analysis and interpretation of data. The current absorbance system is too slow, particularly compromising data analysis for viral and vaccine samples. Current software is unable to index the thousands of data files generated, and does not record experimental setup or protocol, operator identification, or changes in the instrument conditions during an experiment, all of which can lead to confusion and errors when analyzing the results. Overcoming these limitations will allow ultracentrifugation to be used for analysis of larger particles and more complicated interacting systems. A prototype rapid-scan absorbance system has been developed that addresses these issues with a retrofit for existing instruments and vastly improved data acquisition and manipulation software. Work funded by this proposal would bring the prototype to commercial grade and integrate the hardware and software with the recently released fluorescence detection optical system. This work has the support of the base instrument manufacturer, academic researchers and pharmaceutical scientists.